A powerful bomb exploded in a crowded underground walkway in Moscow just yards from the Kremlin yesterday, killing seven people and injuring dozens of other shoppers and evening rush-hour commuters.

The bombing, in the Pushkin Square underpass, was immediately called an act of terrorism, with suspicion falling on rebel fighters in Chechnya.

Early today Russia’s domestic-security agency said it had detained two young men in connection with the blast, one of them a Chechen. The other suspect is from Dagestan.

The Chechen rebels this week are marking several symbolic anniversaries, and have vowed to take their war for independence to the streets of Moscow and other Russian cities.

President Vladimir Putin, who rose to power amid the brutal military crackdown on Chechnya after the devastating bombings of Moscow apartment buildings a year ago, convened an emergency meeting of his top security advisers last night, and has taken direct control of the investigation.

“This explosion has deeply shaken Russia,” Putin said in a statement. “I share the pain of all of those whose nearest and dearest died as a result of this terrifying tragedy.”

Police believe the bomb was a homemade device that was placed on the ground near a theater kiosk and deliberately set off at a time when Moscow’s busiest passageway was jammed with rush-hour commuters.

Reports from the scene described a chaotic, hellish situation in which people staggered out of the smoldering passageway entrance – their clothes ripped, some missing limbs and others with their faces covered with blood.

“I heard a roar. In the first second, I could not understand what had happened. Then I saw injured people,” commuter Yevgeny Karamyan told Western news agencies.

Moscow Mayor Yuri Luzhkov said 51 people were injured – 11 seriously. The bombings came as Russian security forces in Chechnya and other regions were in a heightened state of alert because of intelligence reports that the Chechen rebels were planning a new offensive.

This month marks the fourth anniversary of the Chechen declaration of independence after Russian forces retreated from Grozny – the breakaway republic’s capital – in the 1994-1996 war. It is also the one-year anniversary of the start of the second Chechen war, when rebels attacked neighboring Dagestan and proclaimed it an Islamic state.

“Neither the regular Chechen forces nor the special services nor the warlords have anything to do with the explosion in Pushkin Square,” Maskadov said.

Last month, Chechen suicide bombers staged a series of devastating attacks on several Russian military posts inside Chechnya. And rebel commanders, who are switching tactics after being routed by Russian forces, have declared that they have two battalions of bombers standing in the wings ready to carry out the war beyond Chechnya’s borders.

Russian Interior Ministry forces also seized a large pack of explosives believed to be intended for Chechen rebels in the southern Russian city of Ryazan yesterday, according to Russian media reports.